1. Field of the Invention
The present invention relates to a data processing apparatus, and more particularly to a data processing apparatus of the microprogram controlled system operative in response to a microinstruction so as to sequentially and repeatedly select a plurality of registers. More specifically, the present invention relates to a data processor effectively used in a disc memory controller.
2. Description of Related Art
In the conventional data processing apparatus of the above mentioned type, once one microinstruction is executed, individual registers contained in a register group are sequentially selected one by one, but only one round. For example, assuming that two registers A and B are provided, the two registers A and B are sequentially selected as follows with the execution of one microinstruction.
REGISTER A PA1 REGISTER B PA1 REGISTER A PA1 REGISTER B PA1 REGISTER A PA1 REGISTER B PA1 REGISTER A PA1 REGISTER B
In the conventional data processing apparatus, however, a sequential cyclic one-by-one selection of all individual registers cannot be repeated several times with the execution of one microinstruction. For example, in the case of two registers A and B being provided, the following selection cannot be executed with the execution of only one microinstruction.
Therefore, in the case that a test pattern "4489 H" is processed continuously three times, as in processing of address marks in a flexible disc memory, it is indispensable to prepare three microinstructions, each of which causes to execute the processing of "4489 H", so that the pattern "4489 H" is sequentially and continuously executed three times.
As seen from the above, when the operation in which a plurality of individual registers are sequentially selected one by one and one cycle should be repeated several times in the conventional data processing apparatus, it is necessary to prepare microinstructions of the number corresponding to the number of repetitions of the above mentioned operation. As a result, the amount of microinstructions in the data processing apparatus is inevitably increased. In other words, the degree of freedom in the system design is limited in this regard.